The present invention relates to an inspection method to evaluate welding condition. The inspection method transmits ultrasonic pulses to a slit as a incomplete penetration in the groove weld zone of a flange and a web.
The inspection method by ultrasonic testing is widely known as a conventional method to evaluate welding condition in the groove weld zone of the flange and the web. The inspection method, which transmits ultrasonic pulses to an object for inspection and then measures the echoes, can specify the location and size of reflection sources in the object based on the echoes. However, the inspection method can not specify the shape, size and angle of flaws precisely in the object.
Generally, the inspection method estimates roughly the size of the each flaw based on the maximum echo and estimates the length of the each flaw as a ultrasonic flaw length based on a dimension where a certain level of the echo is measured. Thus, the inspection method can not measure precisely the depth of the flaw. A new inspection method, which can measure precisely the depth of the flaw, is expected.
As a conventional inspection method to evaluate welding condition in the weld zone, the single probe technique, as disclosed in, for example, Japanese Patent Application KOKAI Publication No. 60-57250 and Japanese Patent Application KOKAI Publication No. 2000-310521, is known.
The inspection method, disclosed in the KOKAI Publication No. 60-57250, transmits ultrasonic pulses from the probe to the weld zone at an angle of 70 degrees, receives the echoes, measures the time and the echo height, and calculates the location of reflection sources by mean of the trigonometric function based on the measured time and the echo height.
However, it is very difficult to acquire high-precision data by this inspection method because this inspection method estimates the location of the reflection source, scans on every side with the probe, and determines the flaw by the echo height. And, although it is comparatively easy to measure the length of the flaw in line with the weld zone, it is very difficult to measure the depth of the flaw by this inspection method because there is no clear inspecting standard and the echoes return from not only the flaws. An experienced operator is required for this inspection method.
Moreover, the inspection method disclosed in the KOKAI Publication No. 2000-310521 is the single probe technique. This inspection method measure the length of an unwelded zone at the point where the maximum echo is measured by transmitting the ultrasonic pulses from the probe, which moves backward and forward on the web, and by receiving the echoes returned from the unwelded zone to the probe. In the Publication, the inspection method is described as the method using the relation that the height of the maximum echo is relative to the length of the unwelded zone.
However, in this inspection method, the echo height does not only depend on the length of the unwelded zone but highly depends on the condition of the contact faces of the flange and the web, such as surface-roughness at the unwelded zone, or the size of a slit when there is a slit at the unwelded zone. Since the condition and the size of the slit cause errors in measuring the length of the unwelded zone by the echo height, this inspection method can not measure precisely.
This inspection method transmits ultrasonic pulses from the end face of the flange to the unwelded zone, and calculates the length of the unwelded zone based on the difference of the arrival time of both echoes, one is returned from the end of the unwelded zone at the tip side of the groove, and the other is returned from the bottom side of the web.
This inspection method measures the length of the unwelded zone by digitizing the echoes and by calculating its digitized numerical values based on certain formulas because the difference of the arrival time of the both echoes is very small. Thus, this inspection method requires accurate processing and special measuring devices, and raises its costs.
Meanwhile, with respect to the evaluation of the quantity of a penetration at the weld zone, a method is conceivable that the actual quantity of the penetration is determined by the information of a incomplete penetration (the slit) by means of the angle beam method with the probe from the outer surface of the web. In this method, a technique is required to recognize the difference of the size of the slit by 0.1 mm.
At the slit, the diffusion and incidence angle of the ultrasonic pulses are important issues because it is difficult to identify the size of the slit and the echoes returned from the slit.
Therefore, a problem that has to be solved is to obtain the best combination, such as the combination of the transducer of the probe, the ultrasonic frequency, the testing position, and the incidence angle of the ultrasonic pulses, etc.